Photophysical properties and estimation of ground and excited state dipole moments of 7-diethylamino and 7-diethylamino-4-methyl coumarin dyes from absorption and emission spectra

In the present work, the effect of solvents on absorption and fluorescence spectra and dipole moments (μg, μe) of 7-diethylamino coumarin (7DEAC) and 7-diethylamino-4-methyl coumarin (7DEA4MC) have been studied in different solvents of various polarity at room temperature. The solvents have been selected in a way to cover the full range of intermolecular interactions from non-polar hexane to strongly polar formamide. Using the methods of solvatochromism, the difference in the first excited singlet-state (μe) and ground state (μg) dipole moments was estimated from Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet and McRae equations. The Onsager’s cavity radius of the probes has been calculated by AM1 and PM3 quantum chemical calculations and also by a direct relation. The change in dipole moment value (Δμ) was also calculated by using the variation of Stoke’s shift with microscopic solvent polarity parameter (ETN). The calculated dipole moments represent new results, as well as some of the solvatochromic results that were not studied earlier in such large number of solvents. It is observed that the values of excited singlet-state dipole moments are higher than the ground state ones in both the molecules, which shows that excited states are more polar than the ground states

Determination of excited singlet-state dipole moments of hydroxy and methoxy coumarins using solvatochromic method

The effects of solvents of various polarity on the electronic absorption and fluorescence spectra of 7-hydroxy-4-trifluoromethyl coumarin; 6,7-dihydroxy-4-trifluoromethyl coumarin and 7-methoxy-4-trifluoromethyl coumarin have been investigated. The singlet-state excited dipole moments (μe) and ground state dipole moments (μg) are estimated from Bakshiev and Kawski-Chamma-Viallet equations by using the variation of Stokes’ shift with the solvent’s dielectric constant (ε) and refractive index (n). The observed singlet-state excited dipole moments are found to be larger than the ground-state ones. In addition, the geometry and other electronic properties are computed using ab-initio method with correlation functions at 6-31G basis set